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An autonomous signal for basolateral sorting in the cytoplasmic domain of the polymeric immunoglobulin receptor

J E Casanova1, G Apodaca, K E Mostov

  • 1Department of Anatomy, University of California, San Francisco 94143.

Cell
|July 12, 1991
PubMed

Insights

A specific 14-amino acid sequence in the polymeric immunoglobulin receptor directs it to the basolateral surface of epithelial cells. This sequence acts as an autonomous signal for basolateral sorting, not a default process.

Area of Science:

  • Cell biology
  • Molecular biology
  • Epithelial cell biology

Background:

  • The polymeric immunoglobulin receptor (pIgR) is crucial for transporting polymeric IgA and IgM.
  • pIgR is normally delivered from the Golgi to the basolateral surface of epithelial cells.
  • This transport is essential for mucosal immunity.

Purpose of the Study:

  • To identify the specific region of pIgR responsible for its basolateral surface localization.
  • To determine if this region contains an autonomous sorting signal.
  • To investigate the mechanism of pIgR sorting from the Golgi apparatus.

Main Methods:

  • Site-directed mutagenesis to create a pIgR mutant lacking a 14-amino acid segment.
  • Analysis of protein localization using immunofluorescence microscopy.
  • Assessing the effect of the identified sequence on the localization of a heterologous protein (placental alkaline phosphatase).

Main Results:

  • A 14-amino acid segment in the cytoplasmic domain of pIgR directs it to the basolateral surface.
  • A mutant pIgR lacking this segment is sorted directly to the apical surface from the Golgi.
  • This 14-amino acid sequence is sufficient to redirect an apical protein to the basolateral membrane.

Conclusions:

  • The identified 14-amino acid sequence contains an autonomous signal for sorting to the basolateral plasma membrane.
  • Basolateral sorting of pIgR is not a default pathway but is actively regulated by a specific signal.
  • This finding provides new insights into the mechanisms of protein trafficking in epithelial cells.

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